1. Field of the Invention
The present invention relates to digital communication systems, and more particularly pertains to a system that employs spread spectrum techniques for signal transmissions.
2. Description of the Prior Art
The use of spread spectrum techniques for the transmission of signals by radio, radar, television, etc. is well known. It is generally understood that spread spectrum communication systems have a number of advantages over other systems. For example, spread spectrum communication systems are particularly useful in resisting external interference, operating with low energy spectral density, providing multiple-access capability without external control, and making it difficult for unauthorized receivers to observe the message. Clearly, in the past, many of these features have made the use of spread spectrum techniques of special importance in military communications. Important non-military applications of spread spectrum communication have also been proposed.
For instance, because a plurality of spread spectrum systems can operate without mutual interference, the Federal Communication Commission (FCC) has encouraged its commercial use by designating a frequency band over which unlicensed operators may transmit properly generated spread spectrum signals. One important processing standard set by the FCC is the amount of randomizing required in the spread spectrum transmissions. The FCC has specified that the transmissions should have a degree of randomness similar to that of a code having at least some specified number of chips, presently this number is 127 chips. Of course, the randomness standard is important for all spread spectrum systems if interference is to be avoided when using the same or adjacent bands.
One of the most critical problems confronting designers of digital communication systems that employ spread spectrum techniques is to accomplish the required randomness while conserving bandwidth and increasing bit transmission speed. The present invention fulfills this need.